Downhole drilling spotting fluid composition and method

ABSTRACT

An aqueous-based composition comprising a glycerophosphoric acid ester and a diacetyltartaric acid ester of mono and/or diglycerides when combined with viscosifier, sealant and weighting agent is suitable for use as a spotting fluid for downhole drilling operations for releasing stuck drill string. The present invention also enhances drill fluid lubricity, is nontoxic to marine life, non-polluting and may be safely disposed of in off-shore waters.

This is a divisional of copending application 07/657,113 filed on Feb.19, 1991 now U.S. Pat. No. 5,127,475 which is a continuation ofapplication 07/532,261 filed on Jun. 1, 1990, now U.S. Pat No.5,002,672.

FIELD OF THE INVENTION

The present invention relates to a spotting fluid and method fordislodging a drill string during downhole drilling operations, and moreparticularly to an aqueous-based spotting fluid and lubricant.

BACKGROUND OF THE INVENTION

In the art of boring into the earth with a drill string, particularlyfor oil and gas production, the drill string periodically becomes lodgedwithin a subsurface formation. Failure to release the frozen drill pipecan result in an abandonment of the well. In response, spotting fluidswere developed to lubricate the affected area, "spotting" referring tothe placement of a quantity of drilling fluid known as a pill or slugcontaining a release agent at the area of concern. Furthermore,incorporating a lubricating factor into the drilling mud during ordinaryoperation to prevent drill pipe sticking is a common practice.

The composition of these release agents has generally consisted ofvarious kinds of oils such as synthetic oils, vegetable oils, mineraloils, diesel oils and crude oils. Oil-based spotting fluids, however,are generally difficult to prepare because strong agitation is requiredto achieve an oil-water suspension taking much time when time may be acrucial consideration.

Disposal of drilling fluids containing oil components has also comeunder much closer environmental scrutiny and regulation concurrent withincreasing concern about reducing pollutants in ground water and coastalwater environs. Drilling muds containing oil are generally classified aspollutant streams having costly regulated disposal procedures. Such oilsare not in the best interest of marine wild life and may leave anunsightly sheen in the water.

Accordingly, there is an urgent need for a spotting fluid release agentand lubricant in the art of oil and gas production which is nontoxic,non-oil based, inexpensive and easy to prepare and use. The Applicanthas no knowledge of the prior use of an aqueous-based compositioncomprising glycerophosphoric acid esters and diacetyltartaric acidesters of mono and/or diglycerides in the petroleum industry as aspotting fluid and lubricant.

U.S. Pat. No. 4,876,017 discloses a composition of matter comprising asynthetic hydrocarbon compound such as a poly-α-olefin which may becombined with emulsifiers and thinners to serve as a downhole lubricant.The lubricant is said to be nontoxic to marine life. The poly-α-olefinmay also function as a spotting fluid.

Preparation of glycerophosphoric acid ester in its various isomericforms is disclosed in several articles including, Cherbuliez et al.,Helv. Chim. Acta, vol. 29, p. 2006 (1946), Baer et al., Journal ofBiological Chemistry, vol. 128, p. 491 (1939), and Baer et al., Journalof Biological Chemistry, vol. 135, p. 321 (1940).

SUMMARY OF THE INVENTION

The present invention is an aqueous-based drilling fluid compositionthat enhances the lubricity of a drilling fluid to prevent drill stringsticking. The present invention utilized as a spotting agent reduces thetime required to release a stuck pipe. By eliminating the need foroil-based components, the present invention is nontoxic to marine life,environmentally acceptable, easy to prepare, and capable of beingdisposed of at the drill site without costly disposal procedures.

In one embodiment the present invention comprises a spotting fluidconcentrate composition suitable for use in downhole drilling operationsin a pill for releasing periodically stuck drill string. The concentratecomprises a glycerophosphoric acid ester, a polyacyloxy polycarboxylicacid ester of mono and/or diglycerides, an optional viscosifying agentand an optional sealing agent dispersed and/or soluble in water.

In another embodiment, the present invention is a pill compositioncomprising the spotting fluid concentrate and a weighting agent foradjusting the density of the concentrate. The concentrate comprising anaqueous dispersion and/or solution of a glycerophosphoric acid ester, anoptional polyacyloxy polycarboxylic acid ester of mono and/ordiglycerides, an optional viscosifying agent and an optional sealingagent.

In a further embodiment, the present invention comprises a method forlubricating a downhole well drilling operation comprising the steps of:mixing a spotting fluid concentrate with a drilling mud and circulatingthe mud mixture through the well. The concentrate comprising an aqueousdispersion and/or solution of a glycerophosphoric acid ester, anoptional polyacyloxy polycarboxylic acid ester of mono and/ordiglycerides, an optional viscosifying agent and an optional sealingagent. The drilling mud comprises the concentrate in an amount of fromabout 1 to about 15 percent by volume of the drilling mud, preferablyfrom about 3 to about 8 percent by volume of the drilling mud.

In yet another embodiment, the present invention comprises a method formixing a spotting fluid pill, comprising the steps of: mixingglycerophosphoric acid ester with an aqueous dispersion of aviscosifying agent, sealing agent, and an optional polyacyloxypolycarboxylic acid ester of mono and/or diglycerides; and conditioningthe aqueous dispersion with a weighting agent.

In yet a further embodiment, the present invention includes a method forreleasing a stuck drill assembly in a downhole well drilling operationcomprising the steps of: preparing a pill of a spotting fluidcomposition; displacing a drilling fluid in the well with the pill in anamount sufficient to contact the well bore with the pill adjacent thelocation of the sticking; displacing the drilling fluid with anadditional quantity of the pill until the drill assembly is free tomove; and circulating the drilling fluid to incorporate the pill intothe fluid. The pill composition comprises an aqueous mixture of aglycerophosphoric acid ester, an optional polyacyloxy polycarboxylicacid ester of mono and/or diglycerides, an optional viscosifying agent,an optional sealing agent and a weighting agent. The method may alsoinclude vertically working the drill assembly during the initialdisplacing step; and further removing the drill assembly prior to thecirculating step and staging back into the well with the freed drillassembly.

The invention generally comprises the glycerophosphoric acid ester inthe concentrate in an amount of from about 1 to about 60 percent byweight of the concentrate, preferably from about 10 to about 32 percentby weight of the concentrate and optimally from about 18.5 to about 24.5percent by weight of the concentrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention comprises an aqueous-basedspotting fluid concentrate which is nontoxic to marine life, and absentany oil components, is acceptable to water environments, particularlythe coastal waters around off-shore drilling operations. In anotherembodiment, a spotting fluid pill prepared therefrom enhances thelubricity of drilling fluids and effectively frees stuck drill string.Furthermore, the present invention is easy to prepare and cost effectiveto use.

In particular, the preferred embodiment of the present inventioncomprises a water solution of a glycerophosphoric acid ester and adiacetyltartaric acid ester of mono and/or diglycerides to obtain ageneral purpose spotting fluid concentrate. To this concentrate theremay be added, a viscosifier, a sealant and a weighting agent in order todesign a pill specifically conditioned to the drilling operation athand.

The first component of the present invention is glycerophosphoric acidester which may be prepared, for example, as the reaction product ofglycerin and phosphoric acid. Glycerophosphoric acid ester constitutes amud cake dehydrating agent and is the primary component responsible forreducing the adhesion of a mud cake upon the frozen drill string.Glycerophosphoric acid ester typically comprises from about 1 to about60 percent by weight of the concentrate preferably from about 10 about32 percent by weight of the concentrate and optimally from about 18.5 toabout 24.5 percent by weight of the concentrate composition of thepresent invention.

A second component of the concentrate is a reaction product of (a) amono and/or diglyceride with (b) a polyacyloxy polycarboxylic acid. Themono and/or diglyceride is generally an ester of a fatty acid of up toabout 32 carbon atoms with glycerol. The polyacyloxy polycarboxylic acidreactant comprises at least diacyloxy and dicarboxylic acidfunctionality along a hydrocarbon backbone of from 4 to about 18 carbonatoms, preferably from 4 to about 6 carbon atoms. Each acyloxy radicalgenerally comprises up to about 16 carbon atoms, preferably up to about10 carbon atoms, and more preferably up to about 6 carbon atoms. Acyloxyfunctional groups may be the same or different along the hydrocarbonbackbone. An especially preferred polyacyloxy polycarboxylic acid isdiacetyltartaric acid. The diacetyltartaric acid, for example, reactswith a remaining hydroxy group on the mono and/or diglyceride in acondensation reaction. The reaction product of diacetyltartaric acidwith a mono and/or diglyceride (DATEM) is a preferred compound. DATEM iscommercially available, for example, from Grinsted Products, Inc. orGrinsted AG under the tradename PANODAN SD or PANODAN TR. DATEM is aprimary lubricating ingredient in the concentrate reducing friction andadhesive tendencies between the drill string and a wellbore or steelcasing.

DATEM typically comprises from 0 to about 25 percent by weight of theconcentrate composition, preferably from about 0.5 to about 20 percentby weight and optimally from about 0.8 to about 3.5 percent by weight ofthe concentrate composition of the present invention.

Additional components may include viscosifying and sealing agents aswell as minor quantities of other additives having different purposessuch as balancing pH, thinning, defoaming and the like. These componentsare well known in the arts.

The purpose of the viscosifying agent is to enable a solid weightingmaterial to be suspended in the spotting fluid mixture. Suitableviscosifying agents include marine plant gum, terrestrial plant gum,microbial polysaccharide gum and other polysaccharide gum derivatives.Viscosifying agents are available under the trade names KELCO XC, XCD,XANVIS, BIOZAN, and the like. The viscosifying agent typically comprisesfrom 0 to about 8 percent by weight of the concentrate, preferably fromabout 0.1 to about 5 percent by weight and optimally from about 0.4percent by weight of the spotting fluid concentrate.

The addition of a sealing agent may be made in order to provide a solidparticle barrier to transference of fluids from the wellbore into apermeable low pressure formation. Such loss of fluids and wellborepressure may cause a sticking situation. Examples of sealing agentsinclude gilsonite, water dispersible asphalt, calcium carbonate,vegetable fiber and the like. The sealing agent typically comprises from0 to about 10 percent by weight of the concentrate, preferably fromabout 2 to about 8 percent by weight and optimally from about 4 to about7 percent by weight of the concentrate. The remainder of the spottingfluid concentrate comprises a diluent which is preferably fresh water orsea water.

Another embodiment of the present invention comprises spotting fluidpill formulated utilizing the spotting fluid concentrate conditioned bya weighting agent. Examples of weighting agents include barite,hematite, calcium carbonate, and the like. Conditioning criteria includedensity, viscosity, water loss at both ambient and downhole pressure andtemperature, thickness of the cake, and other physical qualitiesimportant in drilling operations and well known in the drilling arts.Matching the physical characteristics of the drilling mud for any givenwell is an important criterion for spotting the pill at a specificwellbore location. Density of the pill is a particularly importantfactor.

                  TABLE I                                                         ______________________________________                                        COMPONENTS OF A ONE BARREL (42 gal) MIX                                                   SPOTTING FLUID                                                    DENSITY (lb/gal)                                                                          CONCENTRATE (bbls)                                                                             BARITE (lbs)                                     ______________________________________                                         8.8        1.000            0.00                                              9.0        0.993            11.16                                            10.0        0.974            39.06                                            10.5        0.936            94.87                                            11.0        0.918            122.77                                           11.5        0.899            150.67                                           12.0        0.880            178.58                                           12.5        0.861            206.48                                           13.0        0.843            234.38                                           13.5        0.824            262.38                                           14.0        0.805            290.19                                           14.5        0.787            318.09                                           15.0        0.768            345.99                                           15.5        0.749            373.90                                           16.0        0.730            401.80                                           16.5        0.712            429.70                                           17.0        0.693            457.60                                           17.5        0.674            485.51                                           18.0        0.655            513.41                                           ______________________________________                                    

The concentration of weighting agent required is generally determinedbased upon conditioning criteria mentioned above. Table I shows theapproximate weight of a common weighting agent, such as barite, requiredto achieve a stated density in the concentrate of the present invention.

Components of the present invention are preferably freshly mixed priorto use in a large vessel or a clean mixing pit. Advance preparation isdiscouraged because glycerophosphoric acid ester is hydroscopic.However, conditioning criteria should be determined in advance so that apill may be prepared without a time delay when needed.

In a preferred manner of practicing the present invention, theglycerophosphoric acid ester component is prepared in a reaction vesselfrom a slow addition of glycerin to a phosphoric acid. In situpreparation of glycerophosphoric acid ester may be less costly thanobtaining a prepared reagent.

The glycerophosphoric acid ester is added to an aqueous dispersionand/or solution of DATEM and viscosifier followed by sealing andweighting agents.

Phosphoric acid is known in the art to have oligomeric structures of theformula H_(n+2) P_(n) O_(3n+1) where n≧1. Examples includeorthophosphoric acid H₃ PO₄ (n=1), pyrophosphoric acid (n=2) and thelike. Any phosphoric acid is suitable for practicing the presentinvention. Widely available and preferred in a compound known aspolyphosphoric acid 115 which comprises a mixture of orthophosphoricacid with higher acids and is sold on the basis of calculated H₃ PO₄content, e.g. 115 percent by weight.

Polyphosphoric acid 115, for example, is combined with glycerin in astoichiometric ratio of about 2:1 of glycerin:polyphosphoric acid 115.This reaction is exothermic and should be undertaken in a suitablereaction vessel by a slow addition of acid into the glycerin so that thereaction temperature preferably does not exceed 160° F. to 170° F. Ifthe addition is too fast, longer cooling time may be required. Thereaction time is typically two hours with an additional hour coolingbefore use. End of the reaction is indicated by the reaction effluenttemperature falling by approximately 20° F.

To prepare a pill, a mixing pit or tank is preferably cleaned to avoidunnecessary contamination. Clean water is pumped through the mixingmanifolds to flush out all the residual drilling mud. Waste water isdumped from the tank and lines. Spotting fluid concentrate and barite orother weighting agent are then mixed in the desired proportions. Thesealing agent is added typically through a mixing hopper concurrent withthe weighting agent for the desired density pill. (The effect of sealingagent on density as shown in Table I is generally negligible for alldensity entries. The hopper discharge is halted and agitated into asmooth fluid.

When it becomes necessary to release a stuck drill string and time iscritical, a spotting fluid pill comprising the aqueous-based concentratesuitably conditioned is prepared. The finished spotting fluid should bepumped down the drill string into the open hole in sufficient quantityto immerse the entire annular interval affected. The pill should bedelivered within 3 to 5 hours for best results. The affected region istypically soaked with the fluid for a time period of from approximately1 to 48 hours, preferably 6 to 30 hours and more preferably 18 to 24hours. An additional quantity of fluid should be pumped periodically toinsure adequate soaking and the string should be worked vertically.Generally, an additional 0.5 to 5 barrels of fluid are pumped per hour,preferably an additional 1 to 1.5 barrels of fluid are pumped, andoptimally about 1 barrel is pumped per hour. When the pipe is free, itis pulled up from the problem zone leaving the spotting fluid tolubricate and seal the low pressure sand formation. The drill string isstaged back into the hole and the drilling fluid is circulated toincorporate the spotting fluid pill as lubricant on the mud. The mud maybe further conditioned with alkalinity control agent, thinner, defoamerand the like as needed.

In another embodiment, the present invention comprises drilling mudpreferably incorporating the spotting fluid concentrate in an amount offrom about 1 to about 8 percent by volume of the drilling mud, generallyin an amount of from about 0.1 to about 25 percent by volume of thedrilling mud. As a lubricating fluid, the present invention reduces theprevalence of drill string sticking. To prepare a lubricating fluid, anaqueous solution of glycerophosphoric acid ester, DATEM, andviscosifying agent is formulated. Component concentrations are the sameas mentioned previously. The lubricating fluid is blended into thedrilling mud, i.e. circulated in the wellbore during drilling.

The present invention is further illustrated by the following examples.

EXAMPLE 1

A spotting fluid pill was prepared by initially formulating theaqueous-based spotting fluid concentrate which is an embodiment of thepresent invention. A 100 barrel (about 4200 gallons) batch ofconcentrate was formulated by slowly adding 1750.8 lbs of polyphosphoricacid 115 to 3440.25 lbs of glycerin in a suitably large vessel underconstant stirring. An exothermic reaction began which raised thetemperature to about 160° F. to 170° F. Approximately 2 hours wasrequired to fully react the polyphosphoric acid 115 and glycerin andcompletion of the reaction was indicated by reaction mixture temperaturecooling by 20° F. or more. Concurrent with the reaction to produce theglycerophosphoric acid ester, 130 lbs of a polymer viscosifier known asKELCO XC, which is a xantham gum, was dissolved in 3736.5 gallons offresh water. Then 295 lbs of DATEM lubricant was added and stirred intosolution. The glycerophosphoric acid ester reaction product was thenadded to the solution of water viscosifier and DATEM and stirred toproduce the finished spotting fluid concentrate. To complete the pill,barite was added together with a water dispersible asphalt sealingagent. The concentration of sealing agent was 15 lb/bbl concentrate(approximately 4 percent by weight of the concentrate).

EXAMPLE 2

A pill was formulated as in Example 1 to test its effects on a stuckdrill string in a well off the coast of Louisiana. The finishedformulated pill, was pumped into the drill string to displace thedrilling mud already there whereby the region of sticking was adequatelysoaked. The pill released the drill string after 2.5 hours of soaking.

EXAMPLE 3

To the same well as in Example 2, the spotting fluid concentrate of thepresent invention was blended into the drilling mud for use as alubricating agent. Beginning with unlubricated mud and then blending thepresent invention to about 4 percent by volume, change in lubricity interms of amps required for drilling was measured. Amp readings werereduced from approximately 650 with the unlubricated mud to about 500with the mud having 4 percent by volume of the present invention.Concentrate composition comprised an aqueous solution of 1.1 percent byweight glycerophosphoric acid ester, 1.2 percent by weight DATEM and 0.4percent by weight viscosifier.

EXAMPLE 4

A sheen test was performed on a sample of spotting aqueous solutionfluid concentrate of the present invention. The composition comprised21.1 percent by weight glycerophosphoric acid ester, 1.2 percent byweight DATEM, and 0.4 percent by weight viscosifying agent in an aqueoussolution. The test was performed according to the test procedures asrecited by the Code of Federal Regulations, 40 CFR part 435 of Aug. 26,1985. In that procedure, a pan having a black liner was filled withreconstituted sea water. Both a 0.15 gram sample and a 15 gram sample ofthe concentrate was placed on the surface of the water and gentlystirred. The components of the concentrate were allowed to diffusethrough the pan of water for about 10 minutes, then a visual observationfor an oil sheen was made. No sheen was observed for either the 0.15gram or the 15 gram sample.

EXAMPLE 5

To the concentrate solution of Example 4, a water dispersible asphaltsealing agent was added to a concentration of about 4 percent by weight(15 lb/bbl concentrate). Further sheen tests were run according to theprocedures of Example 4 and no sheen was observed for both the 0.15 gramand the 15 gram sample.

EXAMPLE 6-7

Toxicity tests were conducted to determine a 50 percent lethalconcentration (LC₅₀) for a drilling mud including two differentconcentrations of the spotting fluid concentrate of the presentinvention. Drilling mud comprised 11.3 lb/gal density lignosulfonate mudcalled generic mud #7. The concentrate comprised an aqueous solution of21.1 percent by weight glycerophosphoric acid ester, 1.2 percent byweight DATEM, and 0.4 percent by weight viscosifier. The proceduresfollowed are those recited in an EPA study entitled "Drilling FluidToxicity Tests", Federal Register, Vol 50, No 165, August 26, 1985.

A 10 percent by volume concentration of the test drilling mud wasprepared in reconstituted sea water having a chloride concentration of20 parts per thousand. The pH was adjusted with diluted hydrochloricacid or dilute sodium hydroxide solution. Both pH and chlorideconcentration were monitored and held constant throughout the 96 hourtest period. One hour after preparing the 10 percent by volume solution,the suspended particle phase (SPP) was decanted. This phase had a milkychocolate appearance. The SPP was further diluted with sea water to formfive different solutions having progressively increasing concentrationof the SPP. A control sample containing just reconstituted sea water wasalso tested. Three repetitions for each SPP concentration were made andthe test results are shown in Table II. Twenty shrimp known asMysidopsis bahia were added to each concentration and repetition for atotal of 360 test animals including the control.

A standard of LC₅₀ toxicity of no greater than 30,000 ppm fordischarging drilling mud at the drill site is generally required.Drilling mud having 3 and 6 percent by volume composition of thespotting fluid concentrate of the present invention easily passed thisstandard with an LC₅₀ varying between about 750,000 ppm to about 830,000ppm of the suspended particle phase.

                                      TABLE II                                    __________________________________________________________________________           CONC. PRODUCT      CONC. SPP.                                                                           MYSIDS                                       EXAMPLE                                                                              (vol. %)  MUD DENSITY                                                                            (ppm)  EXPOSED                                                                             EXPIRED                                __________________________________________________________________________    6      3         11.4      30,000                                                                              60    0                                                                250,000                                                                              60    2                                                                500,000                                                                              60    5                                                                750,000                                                                              60    22                                                               1,000,000                                                                            60    44                                                               control                                                                              60    1                                      7      6         11.4     30,000 60    2                                                                250,000                                                                              60    5                                                                500,000                                                                              60    12                                                               750,000                                                                              60    30                                                               1,000,000                                                                            60    47                                                               control                                                                              60    1                                      8      10                 50,000 20    20                                                               Control                                                                              20    1                                      __________________________________________________________________________

EXAMPLE 8

Further toxicity tests were run according the procedure outlined inExamples 6-7, however, the concentration of spotting fluid formulationin the generic drilling fluid # 7 was increased to about 10 percent byvolume and water dispersible asphalt sealing agent was added at a rateof 15 lb/bbl concentrate. The suspended particle phase of the 10 percentby volume fluid was diluted 1:9 with artificial sea water which wasagain diluted 1:2. Twenty mysids were exposed to both the control andthe diluted SPP for a period of 24 hours. Nineteen of the 20 animalssurvived in the control tests and all 20 survived in the diluted SPPtest (see Table II).

EXAMPLE 9-12

Lubricity testing was performed on several types of drilling mud bothwith and without a 6 percent by volume spotting fluid concentrate of thepresent invention. The concentrate composition comprised 21.1 percent byweight glycerophosphoric acid ester, 1.2 percent by weight DATEM, and0.4 percent by weight viscosifier in an aqueous solution. Othercomponents included a water dispersible asphalt in a concentration of 15lb asphalt per barrel concentrate. The test procedure is known as theBaroid EP lubricity test and the procedure is as follows:

A sample to be tested was placed in the Baroid test equipment comprisinga motor rotating a sleeve in the sample to be tested at fixed rpms and ameans for applying a known amount of torque perpendicular to therotating sleeve. Typically, the torque applying means comprised a woodblock fitted against the rotating sleeve on one side and a torqueapplying wrench on the other. Prior to testing, all the samples were hotrolled in an oven at 200° F. for three hours to simulate temperaturechanges that might occur downhole. The amps required to rotate thesleeve in the mud at a given rpm and a varying degree of torque pressurewas recorded. The lubricity coefficient is a ratio of the amps requiredto the given torque. Results in Table III indicate significant reductionin the amps required to rotate the sleeve and therefore an increase inlubricity in those mud samples comprising 6 percent by weight spottingfluid concentrate.

                                      TABLE III                                   __________________________________________________________________________           CONC. PRODUCT                                                                           MUD             TORQUE                                                                              MOTOR                                  EXAMPLE                                                                              (vol. %)  DENSITY (lb/gal)                                                                        TYPE  (ft-lb)                                                                             AMPS % REDUCTION                       __________________________________________________________________________    9      0         12.3      Ligno-                                                                              100   12                                                                sulfonate                                                                           200   32                                                                      300   43                                                                      400   >50                                                                     500   >50                                                                     600   >50                                           6         12.3      Ligno-                                                                              100   11.5 4.2                                                          sulfonate                                                                           200   28.5 10.9                                                               300   38.5 10.5                                                               400   48   --                                                                 500   >50  --                                                                 600   >50  --                                10     0         12.5      Gypsum                                                                              100   12                                                                      200   24                                                                      300   43                                                                      400   >50                                                                     500   >50                                                                     600   >50                                           6         12.5      Gypsum                                                                              100   10   16.7                                                               200   21   12.5                                                               300   40   7.0                                                                400   49   --                                                                 500   >50  --                                                                 600   >50  --                                11     0         12.5      High lime                                                                           100   10                                                                      200   23                                                                      300   48                                                                      400   750                                                                     500   >50                                                                     600   >50                                           6         12.5      High lime                                                                           100   9    10.0                                                               200   20   13.0                                                               300   22   12.5                                                               400   >50  --                                                                 500   >50  --                                                                 600   >50  --                                12     0         12.6      TEK-mud                                                                             100   10                                                                      200   21                                                                      300   38                                                                      400   >50                                                                     500   >50                                                                     600   >50                                           6         12.6      TEK-mud                                                                             100   9    10                                                                 200   21   0                                                                  300   31   18.4                                                               400   >50  --                                                                 500   >50  --                                                                 600   >50  --                                __________________________________________________________________________

The foregoing description of the invention is illustrative andexplanatory thereof. Various changes in the materials, apparatus, andparticular parts employed will occur to those skilled in the art. It isintended that all such variations within the scope and spirit of theappended claims be embraced thereby.

We claim:
 1. A method for lubricating a downhole well drilling operationcomprising the steps of:(a) mixing a spotting fluid concentratecomposition comprising water soluble glycerophosphoric acid esterprepared as the reaction product of glycerin and phosphoric acid, anoptional viscosifying agent and an optional sealing agent with drillingmud; and (b) circulating said mud mixture through the well.
 2. Themethod of claim 1, wherein said drilling mud comprises said spottingfluid concentrate in an amount of from about 1 to about 15 percent byvolume of said drilling mud.
 3. The method of claim 1, wherein saiddrilling mud comprises said spotting fluid .concentrate in an amount offrom about 3 to about 8 percent by volume of said drilling mud.
 4. Themethod of claim 1, wherein said concentrate comprises saidglycerophosphoric acid ester in an amount of from about 1 to about 60percent by weight of said concentrate.
 5. The method of claim 1, whereinsaid concentrate comprises said glycerophosphoric acid ester in anamount of from about 10 to about 32 percent by weight of saidconcentrate.
 6. The method of claim 1, wherein said concentratecomprises said glycerophosphoric acid ester in an amount of from about18.5 to about 24.5 percent by weight of said concentrate.
 7. The methodof claim 1, wherein said concentrate comprises said viscosifying agentin an amount of from 0 to about 5 percent by weight of said concentrate.8. The method of claim 1, wherein said concentrate comprises saidsealing agent in an amount of from 0 to about 8 percent by weight ofsaid concentrate.
 9. The method of claim 1, wherein saidglycerophosphoric acid ester comprises the reaction product of about 2moles of glycerin per mole of phosphoric acid.